Remote disconnect-reconnect tap for cable television systems

ABSTRACT

A remotely controlled disconnect-reconnect tap for a cable television system having a head end feeding a cable distribution system. The tap comprises means for receiving and detecting a plurality of pairs of tones modulated on a carrier and sent over the cable distribution system from the head end, means responsive to a predetermined sequence of said pairs of tones for developing a control signal, and switch means responsive to the control signal which turns off if already on or on if already off to thereby disconnect or reconnect, respectively, a subscriber to the cable distribution system.

This is a continuation of Ser. No. 486,218 filed July 5, 1974, now U.S.Pat. No. 3,987,398 issued Oct. 19, 1976.

BACKGROUND OF THE INVENTION

Television receivers in cable television (CATV) subscriber homes arenormally connected by a "drop" cable to the distribution cable passingthe residence by means of a passive device called a "tapoff" or simply a"tap". This tap is basically an unbalanced splitter which diverts asmall amount of the television signals to the connected receiver,leaving the bulk of the signal energy to continue on down thedistribution cable. When a CATV system is constructed it has been thepractice to install all of the tapoff devices that are necesary toconnect 100% of the homes passed. It is unlikely that all of the homeswill become subscribers, but eventually it is expected that the majoritywill take the service. For various reasons, primarily technical, it isexpedient to make provision for 100% acceptance.

When a home is connected for the first time, the drop cable isphysically and electrically installed between the television receiverand the tap. From time to time workmen have occasion to disconnect orreconnect this "drop" cable to the tap for several reasons. Sometimes itis at the request of the user, at other times upon instructions from thecable business office, such as in the case of a disconnect fornon-payment of the monthly fees. A reconnect will be done when paymentof arrears is made, or when a new subscriber occupies the sameresidence. It is generally not the practice to remove the drop cablebetween the tap and receiver when a disconnect is made. The electricalconnection is broken at the tap, and the drop cable is physically leftin place.

SUMMARY OF THE INVENTION

Rather than have a workman go out in the field to reconnect a subscriberto a tap, or disconnect a subscriber from the tap, the present inventionprovides means whereby the connection or disconnection of specificsubscribers may be done from the cable company's central office.

Furthermore, the invention may provide a return path (2 way system) toprovide the following advantageous features:

1. The ability to advise the central office that a "disconnect" commandhas been carried out, and therefore

2. Make it possible to audit the CATV system at any given time todetermine the "on" or "off" status of every tap with this feature.

Each individual tap is assigned an identification code number in whicheach digit corresponds to a different pair of tone frequencies. Atypical example of such a numbering plan is the one employed bytelephone companies in the United States and Canada. Furthermore, thetones used can be identical (though they need not be) to the ones usedby the telephone companies for their touch-tone dialing system. Many ofthe special devices and components used for touch-tone dialing arereadily available, and applicable to the system according to theinvention.

Assuming a six digit code is assigned to a tap, and that there are 10different digits possible for each sequence, it is possible to assign999,999 different numbers, or tap addresses. A five digit code wouldresult in 99,999 addresses, four digits in 9,999 addresses, etc. Eachdigit (1, 2, 3, 4, 5, 6, 7, 8, 9, 0) in the address code corresponds toa pair of tone frequencies. When six tone pairs are sequentially sentout over the CATV cable from the central office in the right code theywill change the "on", (or "off") status of the addressed tap to theopposite condition. Each tap is capable of recognizing its own addresscode when it is present, and does not respond to any deviation from thecode.

If a tone pair is received by the remotely controlleddisconnect-reconnect tap which is not in the sequence set for thatspecific tap, but is received after a correct pair or pairs, the unitwill reset to its initial condition after a predetermined period oftime. A correct tone pair sequence that results in the tap being turned"off", will trigger a reporting signal. This signal can be deliveredback to the central office on a two-way CATV system in the upstream, orsub band as an indication that the "off" command has been carried out.If the command is to turn "on" an "off" tap, no reporting signal istriggered but technically it would be possible. Physical space andeconomics would be considerations for such a feature. An "on" situationcan be verified, to some extent, by going through an "off" command, andgetting an acknowledgement indication. The "on" command is given nextresulting in no acknowledgement but it can be reasonably assumed to havebeen carried out. If not the subscriber will inevitably let the centraloffice know.

As the rotatably controlled disconnect-reconnect tap has "active"elements it needs to be powered, and this is conveniently accomplishedfrom the cable which normally carries AC voltages for poweringamplifiers on the CATV system. An insurance feature is provided in theevent of power failure to the remotely controlled disconnect-reconnecttap. This ensures that the "on" or "off" status of the tap is "held"until power is restored.

To operate the remote control tap, all the central office operator needsto know is the subscriber location identification code and send thatcoded signal through the cables of the CATV system. The signal receivedin the remote tap is converted into a plurality of tones, which,occurring in the proper sequence, cause the tap to turn "off" if "on",or "on" if "off". The remotely controlled tap is capable of recognizingand distinguishing its own address (code) out of all the addresses ofthe subscriber locations.

In its broadest aspects, then, the invention provides a remotelycontrolled disconnect-reconnect tap for a cable television system havinga head end feeding a cable distribution system. The tap comprises meansfor receiving and detecting a plurality of pairs of tones modulated on acarrier and sent over the cable distribution system from the head end,means responsive to a predetermined sequence of said pairs of tones fordeveloping a control signal, and switch means responsive to the controlsignal which turns off if already on or on if already off to therebydisconnect or reconnect, respectively, the subscriber to the cabledistribution system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional system block diagram showing the major equipmentat the central office connected to the CATV system.

FIG. 2 is a simplified block diagram of coding equipment at the headend.

FIG. 3 is a chart illustrating how digits may be assigned to tone pairs.

FIG. 4 is a block diagram of a remotely controlled disconnect-reconnecttap according to the invention.

FIG. 5 is a block diagram illustrating in more detail circuits A3, A4and A5 of FIG. 4.

FIG. 6 is a partly block, partly schematic diagram illustrating in moredetail circuits A6, A7 and A8 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, which shows the major equipment at the centraloffice, the heart of the system is a computer 10, such as a generalpurpose minicomputer. A return signal (to be discussed in more detaillater) from the remote controlled tap 12 will be distinguished by thecomputer which in turn can actuate a read out device 13 which could be aCRT display, or a page printer, or both. The computer 10 is connected toan electronic keyboard or typewriter 16 to provide information such asthe customer's address, identification code, and the time and date whenhis tap was shut off. The keyboard can also give instructions to thecomputer at the discretion of a manual operator. Periodically, thecomputer can scan all of the subscriber locations and automatically shutoff the taps of those who have not kept their payments up to date,information regarding which may be fed into the computer by a cardreader 17, for example. When the payment is received the tap is turnedback on again. A sophisticated system may use a card reader computer,programme cassette tapes or punched tapes. The computer 10 also controlsthe tones generator 18 which feeds pairs of tones in predeterminedsequences, depending on the identity of the subscriber, which feed amodulator 20 which is preferably an FM modulator. The FM modulator 20modulates a carrier of, for example, 73.75 MHz and the resultingmodulated signals are sent over line 21 and the CATV system to theremote controlled tap 12 causing the tap to turn "off" if already "on"or "on" if already "off". This determines whether the subscriber 22 canreceive signals from the CATV system over the house drop 23.

The return sub frequency, 29.00 mHz, is separated from the CATV signalsin the VHF/SUB filter 19. The 1 KHz modulating signal is derived in thesub demodulator 14 and checked in the verifier 15 against the tonesgenerator 18. This ensures that the address sent and the taskidentification signal relate to the same address. It can be arrangedthat the tones generator cannot move on to the next address until theverifier confirms that the last address was turned off. The verifierthen passes this to the computer for storage and/or read out 13.

Referring to FIG. 2, tones generator 18 of FIG. 1 comprises seven audiotone generators F1 to F7 which generate tones f1 to f7 to frequencymodulate a VHF transmitter 20 connected directly to the CATV system atthe head end or hub by a coupler 31. The tones are transmitted two at atime, one from a group of three (F1 - F3) and one from a group of four(F1 - F7) and this results in a possible selection of twelve differentpairs of tone frequencies, the tone pairs being selected by switchingmeans generally indicated at 32. Ten of the audio tones are assigned tocorrespond to digits 0 to 9, and two are left in reserve. The codingsystem can be designed for any number of sequential tone pairs dependingon how many different addresses are to be accomodated. In this case, itis assumed that a six digit code will suffice representing 999,999different combinations.

Coupler 31 also, of course, feeds to the subscribers via the CATV systemthe standard CATV TV and FM signals fed from the head end equipmentindicated by reference numeral 33 over line 34.

The VHF transmitter output carrier can be on any suitable frequency inthe 72-76 MHz band as this band is normally unused and available in allCATV systems. For purposes of this description, assume the frequencyused is 73.75 MHz. This carrier then appears on the CATV system as anintegral part of the signal delivered because it is situated between TVchannels 4 and 5.

Referring to FIG. 4, the 73.75 MHz signal is received at the remotelycontrolled disconnect-reconnect tap shown in this diagram through acoupling network 40 from the CATV distribution cable 41. The first stageA1 is an RF amplifier, preferably a solid state 30 dB gain amplifier,tuned to 73.75 MHz. The next stage, FM discriminator A2, detects theaudio tones received. Tone decoder A3 is a bank of seven tone filterswith inputs connected in parallel, each one tuned to one of the sevendifferent frequencies f1 to f7. Tone decoder A3 feeds a digit gate A4which feeds a sequence gate A5 which, in turn, feeds a voltage switchA6. When the proper sequence of tones f1 to f7 is received, voltageswitch A6 produces a control voltage which causes the coaxial RF switchA7 to change state, from "off" to "on" or from "on" to "off", thuscontrolling the feed of TV or FM signals to the house drop from line 42.Voltage switch A6 also, when it turns the coaxial RF switch A7 from "on"to " off" sends a signal to a task identification generator 43 whichsends a signal of, for example, 29.00 MHz back over a line 44 to thecoupling network 40 and thence back to the head end of the CATV system.

Referring to FIG. 5, there is shown in more detail components A3, A4 andA5 of FIG. 4.

The tone decoder, as mentioned above, comprises a bank of seven tonefilters 45 with inputs connected in parallel. When one of the tones f1to f7 is present, the output of the associated filter F1 to F7 goes tozero.

The digit gate A4 comprises a group of six dual input NOR gates. Thesewill only activate individually when both inputs simultaneously receivea "zero" from the filters in A3 to which they are connected. The actualdigits in the code to which the remotely controlled disconnect-reconnecttap will respond is determined at this point by the configuration of theconnections from the seven filters to the dual inputs of each NOR gate.Assume the digits are assigned as follows:

1 to f1 and f4

2 to f2 and f4

3 to f3 and f4

4 to f1 and f5

5 to f2 and f5

6 to f3 and f5

7 to f1 and f6

8 to f2 and f6

9 to f3 and f6

0 to f2 and f7

* to f1 and f7

# to f3 and f7

A chart can be drawn to represent this as shown in FIG. 3.

Assume a six digit number, say 123,480. The dual inputs of the NOR gateswould be connected to the filters as follows, this being theconfiguration of A3 and A4 in FIG. 3:

Nor 1 to f1 and f4

Nor 2 to f2 and f4

Nor 3 to f3 and f4

Nor 4 to f1 and f5

Nor 5 to f2 and f6

Nor 6 to f2 and f7

If the number was 199,990 then the connection would be:

Nor 1 and NOR 2 to f1 and f4

Nor 3 and NOR 4 to f3 and f6

Nor 5 and NOR 6 to f2 and f7

The next thing is to establish the order in which the particularremotely controlled disconnect-reconnect tap recognizes the code digits.NOR 1 output is connected to a flip flow switch FF1 in sequence gateA5.If the output from NOR 1 has been activated by correct digit then FF1will toggle and its output will start to propagate down the chain. Thusif FF1 is toggled its "true" output Q will go high, placing an enablevoltage on the terminal D of FF2. At the same time, the "not true"output Q of FF1 applies a low voltage to one input of NAND gate 1 thusdisenabling it. If the NOR 2 output is readied by the next correct digitthen flip flop FF2 will toggle as a result of an input over line 47 toits terminal C. The circuit will then wait for a third tone pair toready FF3. Six tone pairs, or digits, in the right order will indicateto the next part of the circuit that the digit sequence is correct. Ifhowever, an improper sequence occurs each of the NAND gates 1 to 5 isconnected in such a way that its output will go to 0 (off) after a fewseconds. The sequence gate A5 will reset to its ready position to awaitthe first correct digit of a new sequence. A correct sequence willtoggle FF7, which produces a 20 millisecond duration 5 volt pulse with adual function. The first function is to advise the ensuing circuit A6(in FIG. 6) that the digit sequence is correct. The second function isto toggle NAND gate 6, which will reset the sequence gate A5 to theready position for the next command.

The diodes and capacitors connected to FF7 are simply a timing network,the time constant of which determines the width of the output pulse,e.g. 20 millisecond.

Referring now to FIG. 6, voltage switch A6 simply switches alternatively+12 volts or -12 volts to operate the coaxial RF switch A7. A6 gets itscommand from FF7 (FIG. 5) so that therefore each time a correct digitsequence occurs the coaxial RF switch will reverse its condition from"off" if "on" or "on" if "off".

A supplementary feature of A6 provides for the "on" or "off" status ofA7 to be preserved in the event of power failure to the remotelycontrolled disconnect-reconnect tap. This is done by the use of a relayoperated mechanical switch 51 which holds its last position whetherpower is on or not.

The output pulse from FF7 to the A6 circuit is applied to the relay coil50. This pulls the switch 51 to the +12 V mode. The next command fromFF7, another pulse, will cause the NAND gate 52 to conduct because bothinputs to it are positive in this mode. The output of NAND gate 52 isconnected to the other relay coil 53 via transistor 54 which pulls theswitch 51 to the -12 V mode where it stays until the next pulse.

Switching of A7 is accomplished by the voltage polarity change in aconventional diode circuit 55. The CATV input is connected to one sideof the diode switch at 56, and the house drop to the other side at 57. Avoltage of -12 V on the diode switch A7 will turn off the CATV signal tothe house drop, and +12 V will turn it on. That is, a positive voltageapplied to the junction of the two back-to-back diodes will cause themto conduct, turning on the switch, and in turn the drop. However, anegative voltage will cause the two back-to-back diodes to stopconducting while the diode in the middle will conduct to ground, causingthe switch to open.

The -12 volts is also used to trigger the task identification generatorA8. This comprises an RF oscillator 60, a modulating signal source 61and a timer 62. The RF oscillator 60, which may be any conventionalcrystal controlled RF oscillator, can provide any frequency in theunused portion of the spectrum of a 2-way CATV system such as, forexample, 29.00 MHz. The modulating signal can be an audio frequency suchas 1 KHz. The timing circuit 62 is used to briefly turn on this AMtransmitter for as long as it is necessary for the information to berecorded at the central office. The output of A8 is coupled back to theCATV distribution cable via line 44 and coupling network 40 where theVHF CATV signals entered the remotely controlled disconnect-reconnecttap. (See FIG. 4).

The diode, resistor and capacitor coupling A7 to A8 are used to producea pulse when the tap is turned off. This pulse keys the timer 62 whichturns on the oscillator 60 for a predetermined length of time.

It will be appreciated that various modifications may be made withoutdeparting from the spirit and scope of the invention as defined in theclaims. An alternative type of logic circuitry which could be used isdigital multiplexing and a binary counter. The first digit would appearat the output from the tone filter and pass through the multiplexer, ifcorrect, causing the counter to advance to position one. This would alsoreprogram the multiplexer to look for the second digit of the desiredsequence. If the next digit received and sampled was correct, the binarycounter would advance to position two and so on. If, however, a digitappeared that was not in the sequence programmed, it would not passthrough the multiplexer and, instead of advancing, the binary counterwould reset to its initial condition.

What I claim as my invention is:
 1. A remotely controlled disconnect-connect system for a cable television distribution system having a head end feeding a cable distribution system, the disconnect-connect system including a plurality of taps disposed at diverse locations along the cable distribution system and connected to a plurality of television receivers, said taps being remote from said television receivers, each tap comprising means for receiving and detecting a time sequence of digit representing signals forming a multi-digit identification code number, each of said digit-representing signals comprising at least one tone modulated on a carrier and sent over the cable distribution system from the head end, means solely responsive to the receipt of the particular sequence of said digit-representing signals forming a predetermined multi-digit identification code associate with said tap for developing an internal control signal, and bistable switch means to connect the cable distribution system and a subscriber's television.
 2. A tap as claimed in claim 1 wherein said bistable switch means comprises a bistable relay which changes state, each time it receives said control signal, between a first and second position, said relay when in the first position toward biasing diodes in a coaxial switch whereby it is "on" and connecting said receiver to the cable distribution system, and in the second position, back-biasing the diodes whereby it is "off" and disconnecting said receiver from the cable distribution system.
 3. A tap as claimed in claim 1 wherein said multi-digit identification code number comprises a multi-digit decimal number, each of said digit-representing signals corresponding to a decimal digit of said decimal number.
 4. A tap as claimed in claim 3 wherein each of said digit-representing signals comprises a pair of tones modulated on a carrier and sent over the cable from the head end.
 5. A tap as claimed in claim 4 wherein said tones are frequency modulated on said carrier and said means for receiving and detecting the pairs of tones comprises an R.F. amplifier having an input connected to the cable system and an output feeding a plurality of tone filters. 